A closure panel assembly, as is typically employed to define a rearward-facing window or “backlite” for a passenger compartment of a light truck, generally includes a fixed glass panel in which an opening is defined, and a sliding glass panel that moves along a pair of support or guide rails between a closed position and an open position relative to the opening. A compression seal is disposed between the fixed and sliding panels, for example, by mounting the seal about the periphery of the opening in the fixed panel. A lateral force, exerted on the sliding panel by the guide rails, ensures that the seal is compressed sufficiently to resist leakage of air and/or water between the fixed panel and the sliding panel when the sliding panel is moved to the closed position. Unfortunately, the lateral force exerted on the sliding panel by the guide rails typically generates a friction drag that resists free and easy movement of the sliding panel across the surface of the seal, thereby making it more difficult for a vehicle passenger to move the sliding panel between the closed and open positions.
What is needed is a means to incorporate a feature into the sliding panel and/or a guide rail to effect a desired compression of the seal disposed between the sliding panel and the fixed panel when the sliding panel is in the closed position, yet allow for sufficient unloading of the seal when the sliding panel is in the open position such that relatively free and easy sliding motion is effected.